CN102014461B - Frequency-sweeping method and device used for TD-LTE (Time Division-Long Term Evolution) - Google Patents
Frequency-sweeping method and device used for TD-LTE (Time Division-Long Term Evolution) Download PDFInfo
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Abstract
The invention relates to frequency-sweeping method and device used for TD-LTE (Time Division-Long Term Evolution). The method comprises the steps of: after obtaining synchronizing information, setting a time domain range and a frequency domain range of data receiving according to the time frequency characteristics of a TD-LTE synchronizing signal for avoiding the influence of an uplink signal, and receiving data of a plurality of possible frequency points once in the frequency domain range of MHz level; converting the received data from a time domain to a frequency domain; measuring the signal intensity in the range of the synchronizing signal and matching frequency domain characteristics, wherein the matching of the frequency domain characteristics can improve the accuracy of the measurement, and avoids the influence of downlink service data on a measuring result; and rapidly selecting the frequency points. Therefore, the invention can improve the searching speed and the searching accuracy of the frequency.
Description
Technical Field
The present invention relates to a long term evolution (TD-LTE) scheme of TD-SCDMA, and more particularly, to a frequency sweeping method and apparatus for TD-LTE.
Background
In the terminal operation process, PLMN (Public Land Mobile Network) search is an important function that must be supported, that is, the terminal actively searches for surrounding Network conditions without prior knowledge and prompting information, and by parsing all PLMN identifiers (PLMN _ Id), arranges out an available PLMN List (PLMN _ List) and reports the List to the user so as to implement a manual Network selection process.
In the processes of initial search of a terminal starting cell, PLMN background search in the operation process and the like, frequency sweeping is needed to be carried out firstly, and frequency points with possible signals are accurately discriminated and sequenced as soon as possible, so that the range is narrowed, and omission and misjudgment are avoided. The key to this process is speed and accuracy.
Compared with the traditional 2G/3G access technology, an important change of TD-LTE is that the bandwidth is variable, and therefore, one characteristic is that the central frequency points of adjacent cells can not be restricted by the bandwidth. In the protocol, the minimum interval between the center frequency points of two cells is 100KHz, and the frequency band often reaches 100MHz (such as 2300 MHz-2400 MHz), which means that the number of center frequency points to be screened in the PLMN search process is as high as 1000. The speed of known frequency sweeping methods is therefore challenged by the large search range.
In addition, TD-LTE is a TDD (Time division Duplex) system. As with all TDD systems, uplink interference is an unavoidable problem. During the frequency sweep, the terminal must perform continuous data reception for a long time in order to search for and identify the network. In this process, the received data is inevitably mixed into the uplink transmission signals of other surrounding terminals, thereby causing the received data to be contaminated. In the conventional frequency sweeping method, an intolerable error is introduced into a measurement result of each frequency point, so that the accuracy of a frequency sweeping result is influenced, and the correctness and the effectiveness of a subsequent result are directly influenced.
The current PLMN frequency sweeping method is described in detail below to analyze its drawbacks.
Referring to fig. 3, the current PLMN frequency sweeping process is completed by the following steps:
in step S10, all possible center frequency points are listed at intervals of 100 KHz. Taking an LTE frequency band of 100MHz as an example, the number of possible center frequency points is 1000;
step S11, continuously receiving data of more than 5ms in the measuring bandwidth range for each possible frequency point;
step S12, calculating the measurement broadband RSSI (Received Signal Strength indicator) of each frequency point;
step S13, if necessary, the measurement bandwidth is changed, and the step S11 is returned;
step S14, counting the broadband RSSI, namely selecting the bandwidth with the most probable frequency point according to the RSSI measured under different bandwidths;
and step S15, counting frequency sweeping results, namely screening all possible frequency points according to the broadband RSSI.
By adopting the known frequency sweeping method, on one hand, the data of more than 5ms needs to be respectively received for more than 1000 frequency points, and the received data of each frequency point needs to be respectively processed to obtain the RSSI, so that the time overhead of sequencing is large; in addition, data for measuring RSSI has blindness in both time domain and frequency domain, influence caused by user data sent by a network and uplink transmission signals of other terminals cannot be avoided, accuracy of sequencing cannot be guaranteed, and further accuracy of subsequent steps is seriously influenced.
Therefore, a reasonable and efficient strategy needs to be found, the accuracy and the rapidity of frequency point sequencing are improved, the user experience is improved, and the network searching performance of the terminal is improved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a TD-LTE frequency sweeping method and device. The method firstly ensures the correctness of the measurement result of each frequency point and reduces the number of the frequency points to be searched on the basis.
One aspect of the present invention provides a frequency sweeping method for TD-LTE, which includes the following steps:
a. acquiring all possible frequency points in an LTE frequency band;
b. acquiring synchronous information;
c. receiving data in a predetermined time domain range based on the synchronization information in a frequency band with a predetermined bandwidth range, wherein no terminal uplink signal exists in the predetermined time domain range;
d. performing frequency domain transformation on the received data to obtain subcarrier frequency domain data in the frequency band;
e. counting the sum of the intensities of 72 subcarriers around the frequency point in the frequency band;
f. performing frequency domain characteristic matching on the frequency points in the frequency band, wherein the frequency points of which the ratio of the sum of the intensities of 62 subcarriers around the frequency point to the sum of the intensities of 72 subcarriers around the frequency point is not less than a preset coefficient are judged to be successfully matched;
g. and c, determining whether the frequency point of the received data covers the whole LTE frequency band, and if not, replacing the frequency band of the received data and returning to the step c.
In the above method, after step g, the method may further comprise the steps of:
h. and screening N available frequency points with the intensity being more than or equal to tau, wherein tau and N are preset parameters.
In the above method, the step of acquiring the synchronization information further includes: determining whether synchronization is currently performed; if the synchronization is carried out, acquiring the synchronization information from the current synchronization; otherwise, searching the synchronous information by using the cell frequency points recorded in the history.
In the method, the predetermined time domain range is 4 symbols from the secondary synchronization signal to the primary synchronization signal in the TD-LTE downlink synchronization signal.
In the method, the predetermined bandwidth is set according to the capability of the terminal.
In the above method, the method of performing the frequency domain transform includes a fast fourier transform.
In the step of performing frequency domain feature matching on the frequency points in the frequency band in the method, the frequency point of which the ratio of the sum of the intensities of the 31 subcarriers around the frequency point to the sum of the intensities of the 36 subcarriers around the frequency point is not less than a predetermined coefficient can be determined as successful matching.
Another aspect of the present invention provides a frequency sweeping apparatus for TD-LTE, including: means for acquiring all possible frequency points in the LTE frequency band; means for obtaining synchronization information; means for receiving data in a predetermined time domain range in which there is no terminal uplink signal based on the synchronization information in a frequency band having a predetermined bandwidth range; means for frequency-domain transforming received data to obtain sub-carrier frequency-domain data within said frequency band; means for counting the sum of the intensities of 72 subcarriers around a frequency point within the frequency band; the device is used for carrying out frequency domain characteristic matching on the frequency points in the frequency band, and the device judges that the frequency points with the ratio of the sum of the intensities of 62 subcarriers around the frequency points to the sum of the intensities of 72 subcarriers around the frequency points not less than a preset coefficient are successfully matched; means for determining whether a frequency point at which data is received has covered the entire LTE frequency band; and means for replacing the frequency band of the received data.
Compared with the prior frequency sweeping method, the rapid frequency sweeping method has the following remarkable advantages due to the adoption of the technical scheme: firstly, the time and frequency domain range of data receiving are set, so that the influence of an uplink signal is avoided; secondly, the intensity measurement of a plurality of possible frequency points is completed by one-time data receiving, so that the efficiency can be improved by dozens of times; moreover, the measurement of the signal intensity in the synchronous signal range is matched with the frequency domain characteristics, so that the measurement accuracy is improved, and the influence of downlink service data on the measurement result is avoided. In addition, the parameter configuration of the present invention provides a certain flexibility to adapt to different network environments.
Drawings
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below, wherein:
fig. 1 shows a frequency domain structure diagram of a TD-LTE downlink synchronization signal.
Fig. 2 shows a time domain structure diagram of a TD-LTE downlink synchronization signal.
Fig. 3 shows a flow chart of a conventional frequency sweeping method.
Fig. 4 shows a flowchart of a fast frequency sweeping method according to an embodiment of the present invention.
Detailed Description
The embodiment of the invention describes a method for quickly sweeping frequency, which provides improvements on the aspects of improving the accuracy of the measurement result of each frequency point and reducing the number of the frequency points to be searched on the basis of analyzing the time-frequency distribution characteristics of downlink synchronous signals and physical signals of a TD-LTE system.
It can be understood that the terminal is not necessarily unknown to the network in the network searching process. In reality, the terminal often already obtains synchronization information of at least one cell, but the frequency sweeping of the terminal is triggered due to the recovery of a high-level protocol state or the initiation of manual network searching by a user. In this application, the terminal can actually utilize the acquired synchronization information to improve the speed and accuracy of frequency sweeping.
Some useful conclusions can be obtained by analyzing the downlink synchronization signals of the TD-LTE system. Fig. 1 and 2 respectively show a frequency domain structure and a time domain structure of a TD-LTE downlink synchronization signal, and the TD-LTE downlink synchronization signal can be found to have the following characteristics through analysis of the frequency domain structure and the time domain structure of the TD-LTE downlink synchronization signal:
a) the time domain appearance position takes 5ms as a period, the lengths of a primary Synchronization signal PSS (Primary Synchronization Signal) and a secondary Synchronization signal SSS (Secondary Synchronization Signal) are respectively 1 symbol, the time domain positions of 4 symbols are occupied totally, and a downlink control channel is fixed between the PSS and the SSS;
b) the frequency domain position is relatively fixed: in the range of 72 subcarriers at both sides of the central frequency point, effective information is at the central 62 subcarriers, both sides have guard intervals of 5 subcarriers respectively, and no signal is sent in the guard subcarriers;
c) the method comprises the following steps: the Zadoff-Chu sequence and the derivative sequence thereof have strong relativity;
d) the composition and distribution of the synchronous signals are irrelevant to the system bandwidth;
e) a Downlink (DL) control channel is fixed between a pair of PSS and SSS, and at least 3 symbols on both sides belong to a downlink channel or a space, and are not used as a resource for uplink transmission.
According to the signal structure, if the signals received in the frequency sweeping process can be limited to the downlink channels, the interference of other terminal uplink signals to data reception can be eliminated.
The fast frequency sweep method according to an embodiment of the present invention is described below with reference to fig. 4.
In step S20, all possible center bins are listed at intervals of a predetermined bandwidth. Taking an LTE frequency band of 100MHz as an example, taking 100KHz as an interval, the number of possible center frequency points is 1000;
synchronization information is acquired in step S21-23. First, in step S21, it is determined whether TD-LTE synchronization is performed. If TD-LTE synchronization is not obtained (for example, frequency sweeping occurs at the time of starting up), the method enters step S22, historical cell frequency points recorded before the last time of shutdown are obtained according to information stored in the terminal (for example, stored in an SIM card), and primary synchronization signals PSS and secondary synchronization signals SSS are searched for the historical cell frequency points to obtain LTE frame synchronization; if the frequency point is resident, the method proceeds to step S23, and uses the frame header position of the serving cell as the system synchronization information according to the synchronization characteristics of TD-LTE.
Broadband data reception is performed at step S24. The Received data is the measurement basis of RSSI (Received Signal strength indicator), that is, the basis of frequency point sequencing, and the accuracy and purity of the Received data are the guarantee of obtaining correct measurement results. For this purpose, the time and frequency domain ranges of the received data are determined as follows:
time domain range: the time domain range of the received data is 4 symbols from SSS to PSS based on the known synchronization information. Namely:
T＝{S0，S1，S2，S3} (1)
where S0 is the last symbol of sub-frame 0 or sub-frame 5, i.e., the S-SCH in FIG. 2, and S3 is the third symbol of sub-frame 1 or sub-frame 6, i.e., the P-SCH in FIG. 2.
From the frame structure of TD-LTE, it can be found that 3 symbols on the left and right sides of the time range described by the above expression (1) are not used for uplink transmission. Therefore, the step can realize accurate measurement on the cells within the range of 128Km without being influenced by the uplink transmission signals of the terminal;
frequency domain range: selecting the bandwidth within the capability range of the terminal as a predetermined range F from the edge of the frequency bandBFrequency band F of (1). Namely:
F＝{f(i)，f(i)+FB}，f(i+1)＝f(i)+FB (2)
wherein F (i) is the initial frequency point of the ith reception, and the initial frequency point is increased by F each time the data bandwidth is updated in step S30B。
Because the TD-LTE terminal must support the variable bandwidth setting with the upper limit of 20MHz, the terminal has the capability of receiving data in the 20MHz bandwidth range at one time, and the subsequent operation realizes the measurement and sequencing of possible frequency points in the 20MHz bandwidth range. Namely, one-time data receiving, 200 frequency point sequencing in the 20MHz range can be completed. For the frequency point sequencing of the 100MHz frequency band, the data can be completed only by 5 times of data receiving.
It is to be understood that the predetermined bandwidth range of 20MHz described above is not intended as a limitation. In an alternative example, data reception may be performed 10 times at a data reception in the 10MHz range, although the terminal still supports the 20MHz bandwidth setting.
The frequency domain transform is performed at step S25. One method is to perform 2048-point FFT (fast fourier transform) on the received data to obtain subcarrier frequency domain data in the measurement band range F, where the subcarrier width is 15 KHz.
Thereafter, the sum of the intensities of 72 subcarriers around each center frequency point i in the frequency band F is counted in step S26. Namely:
because the synchronous signals, including the primary synchronous signal PSS and the secondary synchronous signal SSS, all exist in the range of 1.08MHz around the central frequency point, and occupy 72 subcarriers. Therefore, the statistics of the intensities of the subcarriers can reflect the possibility that a synchronization signal exists around one frequency point.
Since there is a certain time difference between the arrival of the signals of the cells at the terminal, when the synchronization signal is received according to the frame timing of one cell, the downlink user data of other cells is likely to be mixed therein. In order to avoid the influence of the downlink data on the measurement result, it is necessary to perform frequency domain feature matching on each frequency point in the measurement frequency band F in step S27. The specific process is as follows:
the synchronization signal occupies a frequency domain resource of 72 subcarriers, but 5 subcarriers exist on both sides as gaps (gaps), and the network does not transmit the synchronization signal therein. Therefore, the frequency domain feature matching can be carried out on each receiving frequency point by utilizing the characteristic. The frequency domain feature matching is carried out by adopting the following method:
wherein, <math>
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</math> representing the sum of the intensities of 62 sub-carriers around each central frequency point i within frequency band F. α is a constant less than 1 and represents the signal proportion of the effective synchronization signal over the entire synchronization bandwidth. The value of alpha can be adjusted according to the actual measurement environment, and the larger the value of alpha is, the stricter the matching condition of the synchronization signal is.
For the frequency points which are not successfully matched, the frequency points are considered not to be matched with the frequency domain characteristics of the synchronous signals and are excluded.
It should be noted that, in an alternative embodiment, the sum of the intensities of 36 subcarriers around each central frequency point i in the frequency band F may be counted in step S26, and in step S27, the ratio between the sum of the intensities of 31 subcarriers around the frequency point and the sum of the intensities of 36 subcarriers around the frequency point is calculated, and this ratio also reflects the characteristics of the synchronization signal, so that the magnitude relationship between this ratio and a predetermined coefficient may also be used as the basis for determining whether the matching is successful.
Optionally, in step S28, frequency point screening is performed to reduce the number of frequency points that need to be operated in subsequent search. And reducing the number of selectable frequency points to a range not greater than N by adopting a strategy of absolute threshold + TopN, thereby finishing the sequencing of the frequency points. The specific process is as follows:
sequencing the strength of the characteristic RSSI of all possible frequency points to obtain any frequency point FiSerial number S ofiAnd constructing an available frequency point set P according to the following principle:
Fi∈P，If RSSI(i)≥τ，and Si≤N (5)
tau and N are preset parameters, tau means the minimum signal intensity of a central frequency point of the real TD-LTE, and N means the maximum value of the number of cells covering the position of the terminal at the same time. The two parameters can be obtained through off-line simulation and network planning, and conditions can be properly relaxed in actual use, namely, the absolute threshold of the signal intensity is reduced and the frequency point search range is enlarged.
It is determined at step S29 whether the sweep covers the entire band, 100MHz for the LTE band. If not, the received data band is replaced in step S30, and the process returns to step S24 to repeat the process. Otherwise, the method proceeds to step S31, where all the sweep results are counted.
Aiming at the problems of overlong time and large error of frequency point sequencing in the TD-LTE system, the embodiment of the invention firstly utilizes the characteristic of synchronous networking of the TD-LTE to synchronously detect only one cell, thereby avoiding multiple synchronous detection processes; then, according to the time-frequency characteristics of the TD-LTE synchronous signals, the time and frequency domain range of data receiving are set, the influence of uplink signals is avoided, and the efficiency can be improved in a multiplied way by completing the intensity measurement of a plurality of possible frequency points through one-time data receiving; and moreover, the signal intensity in the synchronous signal range is measured and frequency domain characteristics are matched, so that the measurement accuracy is improved, and the influence of downlink service data on the measurement result is avoided.
The above advantages can be clearly reflected in practical applications. Taking the frequency band of 100MHz as an example, the number of possible center frequency points is 1000, if the existing frequency sweeping method is adopted, the data reception takes 5 seconds in total, and in addition, the data processing takes about 10 seconds; more importantly, the existing method cannot eliminate the influence of uplink transmission signals and downlink services and cannot ensure the accuracy of measurement. By adopting the method provided by the embodiment of the invention, only 5 times of data reception are needed, 4 symbols are received each time, 20 symbols are counted, and the time is about 1.5 ms; and the steps of time-frequency parameters, FFT, signal measurement, frequency domain characteristic matching and the like of the received data enable the measurement to be accurately carried out aiming at the synchronous signals, the influence of uplink and downlink interference data is eliminated, and the measurement accuracy and the accuracy of subsequent operation are ensured.
Although the present invention has been described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (12)
1. A frequency sweeping method for TD-LTE comprises the following steps:
a. acquiring all possible frequency points in an LTE frequency band;
b. acquiring synchronous information;
c. receiving data in a predetermined time domain range based on the synchronization information in a frequency band with a predetermined bandwidth range, wherein no terminal uplink signal exists in the predetermined time domain range;
d. performing frequency domain transformation on the received data to obtain subcarrier frequency domain data in the frequency band;
e. counting the sum of the intensities of 72 subcarriers around the frequency point in the frequency band;
f. performing frequency domain characteristic matching on the frequency points in the frequency band, wherein if the ratio of the sum of the intensities of 62 subcarriers around the frequency point to the sum of the intensities of 72 subcarriers around the frequency point is not less than a preset coefficient, the frequency point is judged to be successfully matched;
g. and c, determining whether the frequency point of the received data covers the whole LTE frequency band, and if not, replacing the frequency band of the received data and returning to the step c.
2. The method of claim 1, further comprising, after step g, the steps of:
h. and screening N available frequency points with the intensity being more than or equal to tau, wherein tau and N are preset parameters.
3. The method of claim 1, wherein the step of obtaining synchronization information further comprises:
determining whether synchronization is currently performed;
if the synchronization is carried out, acquiring the synchronization information from the current synchronization;
otherwise, searching the synchronous information by using the cell frequency points recorded in the history.
4. The method of claim 1, wherein the predetermined time domain ranges from 4 symbols of a secondary synchronization signal to a primary synchronization signal in a TD-LTE downlink synchronization signal.
5. The method of claim 1, wherein the predetermined bandwidth is set according to a capability of the terminal.
6. The method of claim 1, wherein the method of performing the frequency domain transform comprises a fast fourier transform.
7. A frequency sweeping method for TD-LTE comprises the following steps:
a. acquiring all possible frequency points in an LTE frequency band;
b. acquiring synchronous information;
c. receiving data in a predetermined time domain range based on the synchronization information in a frequency band with a predetermined bandwidth range, wherein no terminal uplink signal exists in the predetermined time domain range;
d. performing frequency domain transformation on the received data to obtain subcarrier frequency domain data in the frequency band;
e. counting the sum of the intensities of 36 subcarriers around the frequency point in the frequency band;
f. performing frequency domain characteristic matching on the frequency points in the frequency band, wherein if the ratio of the sum of the intensities of the 31 subcarriers around the frequency point to the sum of the intensities of the 36 subcarriers around the frequency point is not less than a preset coefficient, the frequency point is judged to be successfully matched;
g. and c, determining whether the frequency point of the received data covers the whole LTE frequency band, and if not, replacing the frequency band of the received data and returning to the step c.
8. A frequency sweeping device for TD-LTE, comprising:
means for acquiring all possible frequency points in the LTE frequency band;
means for obtaining synchronization information;
means for receiving data in a predetermined time domain range in which there is no terminal uplink signal based on the synchronization information in a frequency band having a predetermined bandwidth range;
means for frequency-domain transforming received data to obtain sub-carrier frequency-domain data within said frequency band;
means for counting the sum of the intensities of 72 subcarriers around a frequency point within the frequency band;
the device is used for carrying out frequency domain characteristic matching on the frequency points in the frequency band, and if the ratio of the sum of the intensities of 62 subcarriers around the frequency point to the sum of the intensities of 72 subcarriers around the frequency point is not less than a preset coefficient, the device judges that the frequency point is successfully matched;
means for determining whether a frequency point at which data is received has covered the entire LTE frequency band; and
means for replacing the frequency band of the received data.
9. The apparatus of claim 8, further comprising:
and the device screens out N available frequency points with the intensity being more than or equal to tau, wherein tau and N are preset parameters.
10. The apparatus of claim 8, wherein the means for obtaining synchronization information further comprises:
means for determining whether synchronization has currently been performed;
if synchronization is performed, a device for acquiring synchronization information from the current synchronization;
if not, using historical cell frequency point to search synchronous information.
11. The apparatus of claim 8, wherein the predetermined time domain ranges from 4 symbols of a secondary synchronization signal to a primary synchronization signal in a TD-LTE downlink synchronization signal.
12. The apparatus of claim 8, wherein the predetermined bandwidth is set according to a capability of the terminal.
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| CN103188765A (en) * | 2011-12-29 | 2013-07-03 | 同济大学 | Frequency scanning method used for TD-LTE system |
| CN102769894A (en) * | 2012-07-04 | 2012-11-07 | 上海大学 | Multi-gateway multi-node wireless sensor network and multi-gateway channel selection and node adaptive network access method for same |
| CN104349464B (en) * | 2013-07-29 | 2018-05-15 | 中国移动通信集团公司 | The method and apparatus for send synchronizing signal, determining carrier type |
| CN104170437B (en) * | 2014-01-21 | 2018-11-06 | 华为技术有限公司 | Frequency point measurement control method and base station, user equipment |
| CN105813172B (en) * | 2014-12-31 | 2019-05-10 | 展讯通信（上海）有限公司 | A kind of LTE slave pattern searches the method and system of net |
| CN108024076A (en) * | 2016-10-25 | 2018-05-11 | 晨星半导体股份有限公司 | The signal processing apparatus and its signal processing method at television reception end |
| CN110113801B (en) * | 2018-02-01 | 2020-12-18 | 华为技术有限公司 | Cell residence method and device |
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